1. Field of the Invention
The invention relates in general to actuator control circuitry and, in particular, to a multiple actuator control circuit capable of arranging a plurality of push-pull latching actuators into a plurality of predetermined positions of a prearranged configuration upon the receipt of a single select signal. The circuitry is scalable in that it can arrange any number of actuators into any number of prearranged configurations upon receipt of a separate select signal corresponding to each prearranged configuration.
2. Description of the Prior Art
It is well known in many industries to utilize solenoid type actuators as switches for controlling fluid flow, gas flow, and the like. As new actuator designs have been introduced in order to reduce power consumption, so to has new circuitry been designed to control them. One new actuator design of recent years has been the latching solenoid. The latching solenoid has an advantage in utilizing less power than conventional solenoids.
One circuit for controlling a bistable actuator is disclosed in U.S. Pat. No. 4,409,638 issued to Sturman et al. The control circuit in Sturman is integrated into the actuator that is intended to replace conventional solenoid actuators controlling water flow in such devices as dishwashers, sprinklers, and the like. Compared to conventional solenoid actuators the integrated latching actuator in Sturman consumes substantially less power in the actuated state however the input signal must remain on at all times in order to keep the actuator in position. Maintaining the coil of the actuator in an energized state in order to maintain the actuator in a predetermined position is highly undesirable in applications where available power is generally scarce.
Another circuit for controlling a number of direct current operated solenoid valves is disclosed in U.S. Pat. No. 5,909,353 issued to Alberter et al. Although the circuit in Alberter is primarily designed to reduce power loss by retrieving the magnetic energy stored in the inductive coils of the solenoids when the power is turned off, the solenoids must initially be maintained in an energized state by the power source. Hence, maintaining the solenoids in a given position requires the continuous supply of direct current power to the solenoid. This is undesirable in low power applications.
In recent years, considerable research effort has taken place in the field of electromagnetic devices for space applications. This research has led to the development of energy-efficient, small-envelope, low-weight latching actuators. Uniquely, these devices can maintain their selected position when their inductive coils are disconnected from the power source. As used herein, a xe2x80x9clatching actuatorxe2x80x9d refers to a switching device having at least two positions in which either position, once achieved, can be maintained without the application of a power source. The latching force for the positions of the switch are generally produced by permanent magnets, and switching between positions is accomplished by energizing the coils for a brief period of time at a magnitude sufficient to transfer the actuator armature from one latched position to another. The dual position push-pull inductive solenoid, or bistable actuator, is one example of a latching actuator.
The thrust of the present invention is to provide a highly reliable, energy efficient, scalable control and drive system for latching actuators adapted for use in reduced power applications such as in space. These and other difficulties of the prior art have been overcome according to the present invention.
A preferred embodiment of the energy efficient multiple actuator control circuit according to the present invention comprises a timing-slicing circuit for arranging and processing a select signal into a plurality of staggered pulse signals and a steering logic circuit for receiving the pulse signals and generating corresponding actuator enable signals. An actuator enable signal is generated for each actuator to be controlled and preferably each enable signal has a duration greater than the actuator switching time rating of its corresponding actuator. The circuitry is hardwired in that for a given select signal each actuator is arranged into its own predetermined position. The predetermined positions of all the actuators makeup a prearranged configuration or actuator output. The circuitry is scalable to achieve any multiple of prearranged configurations of the actuators by providing separate select signal path for each prearranged configuration.
In one embodiment the actuators are push-pull latching solenoids having two opposed switch positions. These latching bistable solenoids do not require a constant power source to energize their inductive coils in order to maintain either switch position. Switching from one position to the other only requires the application of a reverse polarity enable signal or pulse. Latching is typically accomplished mechanically or with permanent magnets. These solenoids are well suited for use with the present invention control circuit as they can be activated to either position by the application of a pulse enable signal without the need for a continuous power supply. One such suitable bistable solenoid is disclosed in the U.S. Patent Application filed on even date herewith and identified by Attorney Docket No. 20025. Thus, the present invention control circuit significantly differs from a conventional electronic transistor type switch in that it does not utilize a small input signal to activate a short circuit path for continuous power flow.
A significant advantage to the present invention circuitry is that the select signal can substantially vary in voltage, current, and duration, yet still achieve the desired result of arranging the actuators into the prearranged configuration. This makes the circuitry well adapted for applications where high switching reliability is required yet the power available for achieving such switching varies. Thus the present invention circuitry is well suited for spacecraft applications, remote robotics, and the like.
The control circuit is able to arrange a plurality of actuators into a plurality of predetermined positions by the receipt of a single select signal. The single select signal is preferably a brief direct current pulse signal. Advantageously the select signal does not have to be continuously applied to maintain the actuators in their predetermined positions. The control circuit is able to achieve the desired actuation even when the select signal varies substantially in voltage, current or duration. The circuit is energy efficient as actuation is achieved by the select signal alone without the assistance of an additional power source.
The circuitry of the present invention is capable of accurately arranging the actuators into their predetermined positions in response a single select signal that can vary greatly in voltage, current and duration. The circuitry is scalable in that it can arrange any number of actuators into any number of prearranged configurations upon receipt of a separate select signal corresponding to each prearranged configuration.